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#ifndef __BITFIELD_H__
#define __BITFIELD_H__
#include <stdint.h>
#include <stdbool.h>
#define NIBBLE_SIZE (CHAR_BIT / 2)
#ifdef __cplusplus
extern "C" {
#endif
/* Public: Reads a subset of bits into a uint64_t, right aligned so they may be
* interpreted as a number.
*
* source - the bytes in question.
* source_size - the number of bytes in the source.
* offset - the starting index of the bit field (beginning from 0).
* bit_count - the width of the bit field to extract. This must be less than or
* equal to 64.
*
* Bit fields are positioned according to big-endian bit layout and the data is
* swapped automatically as necessary depending on the compiled architecture.
*
* For example, the bit layout of the value "42" (i.e. 00101010 set at position
* 14 with length 6 is:
*
* 000000000000001010100000000000000000000000000000000000000000000
*
* and the same value and position but with length 8 is:
*
* 000000000000000010101000000000000000000000000000000000000000000
*
* Examples
*
* uint64_t value = get_bitfield(data, data_size, 2, 4);
*
* Returns the value of the requested bit field, right aligned in a uint64_t.
*/
uint64_t get_bitfield(const uint8_t source[], const unsigned int source_length,
const unsigned int offset, const unsigned int bit_count);
/* Public: Return a single nibble from the byte array, with range checking.
*
* source - the source byte array.
* source_length - the total length of the source array.
* nibble_index - the index of the nibble to retreive. The leftmost nibble is
* index 0.
*
* Returns the retreived nibble, right aligned in a unsigned int.
*/
unsigned int get_nibble(const uint8_t source[], const unsigned int source_length,
const unsigned int nibble_index);
/* Public: Return a single byte from the byte array, with range checking.
*
* source - the source byte array.
* source_length - the total length of the source array.
* byte_index - the index of the byte to retreive. The leftmost byte is index 0.
*
* Returns the retreived byte.
*/
unsigned int get_byte(const uint8_t source[], const unsigned int source_length,
const unsigned int byte_index);
/* Public: Copy a range of bits from one bit array to another.
*
* The range does not need to be byte aligned, and the source and destination do
* not have to be the same size (as long as the desitnation has enough room to
* fit the range).
*
* A bit array with regards to this function always has the leftmost bit in byte
* 0, i.e. bit index is the leftmost bit of byte 0. Endianness does not matter.
*
* For example:
*
* unsigned int source[4] = {0x11, 0x22, 0x33, 0x44};
* unsigned int destination[4] = {0};
* copy_bits(source, sizeof(source), 8, 8, destination,
* sizeof(destination), 0);
* // destination[0] == 0x22
* // destination[1] == 0x0
* // destination[2] == 0x0
* // destination[3] == 0x0
*
* Thanks to
* http://stackoverflow.com/questions/3534535/whats-a-time-efficient-algorithm-to-copy-unaligned-bit-arrays
* for the implementation of the algorithm.
*
* source_origin - the source array.
* source_length - the total length of the source array in bytes,
* for range checking.
* source_offset - an offset in bits to start the copy from the source array.
* Specify 0 to start from source_origin.
* bit_count - the number of bits to copy.
* destination_origin - the destination array.
* desitnation_length - the total length of the destination array in bytes,
* for range checking.
* destination_offset - an offset in bits to start placing the copied range into
* the destination array. Specify 0 to start from the beginning of the
* destination. If you are copying a range not aligned on a byte, you
* probably want to set this to a positive offset to right the resulting
* bits in the destination.
*
* Returns true if the copy was successful and false if the range exceeded the
* size of the source or destination, or if the range size negative or 0.
*/
bool copy_bits(const uint8_t* source_origin, const unsigned int source_length,
const unsigned int source_offset, unsigned int bit_count,
uint8_t* destination_origin, const unsigned int destination_length,
const unsigned int destination_offset);
/* Public: Copy a range of bits from one array to another, right aligning the
* result.
*
* This is mostly useful if you want to cast the result to an integer type
* instead of a byte array.
*
* For example:
*
* unsigned int source[4] = {0x11, 0x22, 0x33, 0x44};
* unsigned int destination[4] = {0};
* copy_bits_right_aligned(source, sizeof(source), 8, 8, destination,
* sizeof(destination));
* // destination[0] == 0x0
* // destination[1] == 0x0
* // destination[2] == 0x0
* // destination[3] == 0x22
*
* int value = (int)destination;
* // value == 0x22 == 32
*
* The arguments are the same as copy_bits, but without the destination_offset
* option - that's set automatically to right align the result.
*
* Returns true if the copy was successful and false if the range exceeded the
* size of the source or destination, or if the range size negative or 0.
*/
bool copy_bits_right_aligned(const uint8_t source[], const unsigned int source_length,
const unsigned int offset, const unsigned int bit_count,
uint8_t* destination, const unsigned int destination_length);
/* Public: Copy a range of bytes from one byte array to another.
*
* The source and destination do not have to be the same size (as long as the
* desitnation has enough room to fit the range).
*
* source_origin - the source array.
* source_length - the total length of the source array in bytes,
* for range checking.
* source_offset - a byte offset to start the copy from the source array.
* Specify 0 to start from source_origin.
* byte_count - the number of bytes to copy.
* destination_origin - the destination array.
* desitnation_length - the total length of the destination array in bytes,
* for range checking.
* destination_offset - an offset in bytes to start placing the copied range into
* the destination array. Specify 0 to start from the beginning of the
* destination.
*
* Returns true if the copy was successful and false if the range exceeded the
* size of the source or destination, or if the range size negative or 0.
*/
bool copy_bytes_right_aligned(const uint8_t source[], const unsigned int source_length,
const unsigned int offset, const unsigned int byte_count,
uint8_t* destination, const unsigned int destination_length);
/* Public: Set the a nibble in the given data array to the new value.
*
* nibble_index - the index of the nibble to retreive. The leftmost nibble is
* index 0.
* value - the value to set in the bit field.
* destination - the destination array.
* destination_length - the total length of the destination array in bytes,
* for range checking.
*
* Returns true if the bit_count is enough to fully represent the value, and
* false if it will not fit.
*/
bool set_nibble(const unsigned int nibble_index, const unsigned int value,
uint8_t* destination, const unsigned int destination_length);
/* Public: Set the bit field in the given data array to the new value.
*
* value - the value to set in the bit field.
* offset - the starting index of the bit field (beginning from 0).
* bit_count - the number of bits to set in the data.
* destination - the destination array.
* destination_length - the total length of the destination array in bytes,
* for range checking.
*
* Returns true if the bit_count is enough to fully represent the value, and
* false if it will not fit.
*/
bool set_bitfield(const uint64_t value, const unsigned int offset,
const unsigned int bit_count, uint8_t destination[],
unsigned int destination_length);
/* Public: Return a right aligned bitmask for a uint64_t.
*
* bit_count - the number of bits to mask, right aligned.
*/
uint64_t bitmask(const unsigned int bit_count);
/* Private:
*/
unsigned int bits_to_bytes(uint32_t bits);
/* Private: A union to assist swapping between uint64_t and a unsigned int array.
*/
typedef union {
uint64_t whole;
uint8_t bytes[sizeof(uint64_t)];
} ArrayOrBytes;
#ifdef __cplusplus
}
#endif
#endif // __BITFIELD_H__
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